A wide-gap semiconductor such as silicon carbide (SiC) or a nitride semiconductor has a dielectric breakdown field strength about 10 times higher than that of silicon (Si). For this reason, the wide-gap semiconductors are expected as materials of a power semiconductor device that achieves a high breakdown voltage and low loss and thus outperforms a silicon device. For example, a Schottky barrier diode (SBD) containing SiC has been developed as a power semiconductor device that has a higher switching speed than that of an Si—PiN diode and implements a smaller low-loss power converter.
The SBD has problems of, for example, a large reverse leakage current and a low forward surge current withstand. To the contrary, a JBS diode (Junction Barrier Schottky Diode) and an MPS diode (Merged PiN Schottky Diode), which have both a Schottky junction and a p-n junction, are preferable for reducing the reverse leakage current and improving the surge current withstand.
However, when a wide-gap semiconductor is used, it is difficult to form an ohmic contact with a low resistance in a p-type semiconductor. Hence, the JBS or MPS structure cannot sufficiently improve the surge current withstand. Additionally, in this case, since the resistance of the p-n junction region is high, the forward current can hardly flow in the Schottky junction region.
It is therefore necessary to develop an SBD that is made of a wide-gap semiconductor and can implement a higher surge current withstand and a higher forward current density.